1. Field of Invention
The present invention relates to the field of laminates, and more particularly to porous laminates and their construction.
2. Brief Description of the Prior Art
Textiles are often used in industrial applications. Textiles can be processed to provide characteristics called for by a specific use and can be constructed from natural or synthetic materials. For example, porous materials have been used successfully in the filtration of gaseous, liquid and solid particulate materials. Textiles may be used singly or in a composite material such as a laminate. For example, webs or mats of fiberglass have been employed where concerns of heat resistance, and the need of materials to withstand temperatures of 500.degree. to 1000.degree. F. or higher is essential.
Textiles can be used to form composite materials in conjunction with other materials, including other textiles. For example, laminates can be used in the construction of filtration materials, from coffee pot and food filtration devices to industrial filters. A material that has been used in producing a laminate is glass fibers. At high temperature applications, the glass fibers offer resistance to melting and degradation. In the preparation of composite materials, heat bonding of material layers can be done if the materials are compatible. However, not all materials can be combined with one another due to the variations in physical properties possessed by given substances and materials, and the treatment processes a given material must undergo.
PTFE (polytetrafluoroethylene) is a material which will resist heat and chemical degradation in a number of environments. Porous PTFE therefore, has excellent properties for use as a filtration material. The pore size of the material can be varied to suit particular applications where discriminating removal of particles from a fluid or gas stream is required. Porous PTFE has use as a membranous material. Therefore, it is desirable to bond the PTFE material to a substrate material which can provide the rigidity needed to form a composite which can be used as a filter.
The use of a substrate is limited in the known processes. High temperatures demand the use of substrates such as polyimide, fiberglass, PPS (polyphenylene sulfide) or PTFE compositions. In addition, high temperature bonding processes, in turn, have limitations on the types of materials which can be compatibly combined with one another.
The novel method for producing a composite material described below enables the use of a low temperature material, namely polyacrylonitrile, to be employed to form a filtration composite.